Increased risk of herpes zoster in patients with psoriasis: A longitudinal follow‐up study using a national sample cohort

BACKGROUND/OBJECTIVE Although previous studies reported the relationship between psoriasis and herpes zoster, the number of study is not sufficient to support the conclusions. The purpose of this study was to evaluate the association between psoriasis and herpes zoster. METHODS The data of a nationally representative Korean cohort collected in the Korean Health Insurance Review and Assessment (HIRA) System from 2002 to 2013 were used. Psoriasis was defined ≥ 2 International Classification of Diseases 10th revision (ICD-10) L40 codes. Among them, severe psoriasis was defined as psoriatic medication use, including acitretin, systemic corticosteroid, cyclosporine and methotrexate. Other psoriasis was defined as mild psoriasis. Herpes zoster was defined as ≥ 2 ICD-10 B02 codes or ≥ 1 B02 code with antiviral medication use. Psoriasis patients (n = 11 009) and control participants (n = 44 036) were matched 1:4 by age, sex, income and region of residence. A stratified Cox proportional hazard model was used stratified by age, sex, income and region of residence. Crude and adjusted hazard ratios (HRs) were calculated for the risk of herpes zoster in the total psoriasis group, mild psoriasis group, and severe psoriasis group and compared with those in each matched control group. RESULTS The HR for herpes zoster was higher in the psoriasis group than in control group (adjusted HR = 1.22, 95% CI = 1.12-1.33, P